1. Field of the Invention
The present invention relates to a thermally assisted magnetic head which writes signals by a thermally assisted magnetic recording scheme, a head gimbal assembly (HGA) equipped with this thermally assisted magnetic head, and a hard disk drive equipped with the HGA.
2. Related Background Art
As hard disk drives have been increasing their recording density, thin-film magnetic heads have been required to further improve their performances. As the thin-film magnetic heads, those of composite type having a structure in which a magnetism detecting device such as a magnetoresistive (M) device and a magnetic recording device such as electromagnetic coil device are laminated have been in wide use, while these devices read/write data signals from/onto magnetic disks which are magnetic recording media.
In general, a magnetic recording medium is a sort of discontinuous body in which magnetic fine particles are assembled, while each magnetic fine particle has a single-domain structure. Here, one recording bit is constituted by a plurality of magnetic fine particles. Therefore, for enhancing the recording density, it is necessary to make the magnetic fine particles smaller, so as to reduce irregularities at boundaries of recording bits. When the magnetic fine particles are made smaller, however, their volume decreases, so that the thermal stability in magnetization may deteriorate, thereby causing a problem. An index of the thermal stability in magnetization is given by KUV/kBT. Here, KU is the magnetic anisotropy energy of a magnetic fine particle, V is the volume of one magnetic fine particle, kB is the Boltzmann constant, and T is the absolute temperature. Making the magnetic fine particles smaller just reduces V, which lowers KUV/kBT by itself, thereby worsening the thermal stability. Though KU may be made greater at the same time as measures against this problem, the increase in KU enhances the coercivity of the magnetic recording medium. On the other hand, the writing magnetic field intensity caused by a magnetic head is substantially determined by the saturated magnetic flux of a soft magnetic material constituting a magnetic pole within the head. Therefore, no writing can be made if the coercivity exceeds a permissible value determined by the limit of writing magnetic field intensity.
Proposed as a method for solving such a problem in thermal stability of magnetization is a so-called thermally assisted magnetic recording scheme which applies heat to a magnetic recording medium immediately before applying a writing magnetic field, while using a magnetic material having a large value of KU, so as to effect writing with lowered coercivity. This scheme is roughly classified into magnetic dominant recording and optical dominant recording. In the magnetic dominant recording, the writing is attributed to an electromagnetic coil device, while the radiation diameter of light is greater than the track width (recording width). In the optical dominant recording, in contrast, the writing is attributed to a light-radiating part, while the radiation diameter of light is substantially the same as the track width (recording width). Namely, the magnetic dominant recording and optical dominant recording impart space resolution to a magnetic field and light, respectively.
As such a thermally assisted magnetic head recording apparatus, Patent Document 1 discloses a thermally assisted magnetic head comprising a slider having a magnetic head part in which an optical waveguide is provided at a position near an electromagnetic coil device in the laminating direction of the magnetic head (bit length direction), and a light source unit in which a light source is provided on a light source supporting substrate different from the slider. In this structure, light emitted from a light-emitting device is introduced into the optical waveguide and then is let out from a light exit surface of the optical waveguide within the medium-opposing surface, so as to heat a magnetic recording medium locally. Subsequently, the electromagnetic coil device applies a writing magnetic field to a local area of the magnetic recording medium having lowered the coercivity by the local heating, so as to perform writing.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2006-185548